Welcome to the board. I'm sorry that my opinion is going to be discouraging.
I would think you'd be pushing your luck with a wine almost forty years old. Also, it is difficult to sell bottles in small quantity (some want to buy a case or half a case). If the wine is to have any chance of not being over the hill it would have required cellaring at about 55 degrees with proper humidity to keep the cork from drying out. If I were you, I would open the wine myself and see if it has any flavor left and have another bottle for backup if you are left with vinegar.